1. Field of the Invention
The present invention relates to a system for combining a transmitter and a receiver using a circulator and a method for canceling a transmission signal thereof, and more particularly, to a system for combining a transmitter and a receiver using a circulator and a method for canceling a transmission signal thereof, in which a transmission signal incoming to a receiver together with a reception signal is cancelled by generating a 180xc2x0 phase inverted transmission signal with the same magnitude and delay time as those of the incoming transmission signal, to thereby improve an electrical separation degree of the transmitter and the receiver and simultaneously to reduce volume and cost thereof.
2. Description of Prior Art
In the case that a transmission/reception antenna is commonly used in various mobile communication and wireless communication base stations, relay systems or military communication devices, a conventional system for combining a transmitter and a receiver which is used for smoothly combining the transmitter and the receiver with the antenna uses an expensive component called a duplexer to combine the transmitter and the receiver, in which an electrical separation degree is sufficiently secured during combining the transmitter and the receiver owing to the electrical characteristics of the duplexer.
However, since the duplexer uses a number of dielectric resonators, an electrical loss of the duplexer is considerable. Since the transmission and reception bands are fixed in the duplexer, a pass band frequency is variable. In particular, the duplexer cannot be adapted in a secret conversation communication system which is used in a military communication device whose transmission/reception pass band is inverted frequently.
An example of a conventional transmitter/receiver combination circuit will be described in detail with reference to FIG. 1.
The conventional transmitter/receiver combination circuit uses a duplexer 1 which is connected with an antenna 3, in which a transmission band pass filter 1a and a reception band pass filter 1b for filtering a transmission signal Tx and a reception signal Rx, respectively are integrated into a single body. Here, a sufficient circuitry frequency separation feature can be obtained according to the performance of the respective band pass filters 1a and 1b of the duplexer 1.
However, since the pass bands of the transmission/reception band pass filters 1a and 1b of the duplexer 1 are fixed in the transmitter/receiver combination circuit as described above, the fixed transmission/reception band pass filters 1a and 1b of the duplexer 1 block the transmission/reception bands in the case that the pass band is successively varied and the pass band is inverted, resulting in causing the duplexer not to be used in the transmitter/receiver combination circuit. Also, since the number of stages of the resonators in each band pass filter 1a or 1b of the duplexer increases, signal loss and cost increase due to insertion of dielectric resonators into the pass band.
Another conventional transmission/reception combination circuit shown in FIG. 2 combines a transmitter and a receiver with a circulator 2, in which an antenna 3 is connected to a first end of the circulator 2 in order to increase a separation degree and transmission and reception band pass filters 1a and 1b are connected to second and third ends, respectively.
The circulator 2 transfers a supplied signal without causing an electrical signal loss in an arrow direction of the circulator 2, but has an electrical separation feature in an opposite direction of the arrow. The circulator 2 has a separation degree of 20 dB in general.
As described above, the circulator 2 has a merit capable of securing the separation degree of about 20 dB. However, a large power amplification of a transmission signal Tx is accomplished in a power amplifier (not shown) in a transmitter, then a harmonic component due to the amplification is removed in the transmission band pass filter 1a, and then the resultant signal is emitted toward the antenna 3, while passing through the circulator 2, in which case the high power transmission signal Tx from which 20 dB or so is attenuated in the circulator 2 is input to the receiver circuit from the circulator 2 together with the reception signal Rx.
Here, if a transmission signal Tx whose signal power is relatively strong is input to a low noise amplifier (not shown) of the receiver together with a reception signal Rx, the low noise amplifier does not perform a smooth operation and is in saturation state to thereby lose performance of the amplifier.
Thus, the separation degree of the 20 dB or so is considerably insufficient in view of stability of the transmission/reception communication system.
Finally, the conventional FIG. 2 technology should add transmission and reception band pass filters 1a and 1b in order to supplement the insufficient frequency separation degree as in the FIG. 1 technology. In this case, since the number of stages of the resonators in each band pass filter should be increased in order to obtain a sufficient separation band, a loss in the pass band occurs.
Further, since the pass bands of the transmission and reception band pass filters are fixed, the fixed transmission/reception band pass filters 1a and 1b of the duplexer 1 block the transmission/reception bands in the case that the pass band is successively varied and the pass band is inverted, resulting in causing the duplexer not to be used in the transmitter/receiver combination circuit.
To solve the prior art problems, it is an object of the present invention to provide a system for combining a transmitter and a receiver using a circulator and a method for canceling a transmission signal thereof, in which a transmission signal incoming to a receiver together with a reception signal is cancelled by generating a 180xc2x0 phase inverted transmission signal with the same magnitude and delay time as those of the incoming transmission signal, in a transmission/reception common antenna system, to thereby improve an electrical separation degree of the transmitter and the receiver, to reduce a coupling loss and simultaneously to reduce volume and cost thereof.
It is another object of the present invention to provide a system for combining a transmitter and a receiver using a circulator and a method for canceling a transmission signal thereof, in which a high power transmission signal input to the receiver is efficiently cancelled in a transmission/reception common antenna system, and thus a low power variable filter can be used, to accordingly secure a sufficient separation degree between the transmitter and the receiver although a transmission/reception frequency band such as a secret conversation communication is inverted or changed.
It is still another object of the present invention to provide a system for combining a transmitter and a receiver using a circulator and a method for canceling a transmission signal thereof, which is included in the receiver and can greatly attenuate a noise signal level of a reception band which is generated from the transmitter and input to the receiver.
To accomplish the above object of the present invention, there is provided a transmitter/receiver combination system for combining a transmitter and a receiver into a single antenna in a wireless communication system, the transmitter/receiver combination system comprising: a circulator for receiving a transmission signal from the transmitter, transmitting the received transmission signal to an antenna without causing a signal loss, and transmitting a reception signal received from the antenna to other ends without causing a signal loss; and at least one transmission signal canceller for dividing the transmission signal input in an attenuated form as much as a predetermined magnitude via the circulator together with the reception signal into at least two paths, producing two mutually phase inverted transmission signals with the same magnitude and delay time as those of the incoming transmission signal, and recombining the produced two transmission signals with each other, to thereby canceling the transmission signal and transmitting only the reception signal to the receiver.
In the present invention, the transmission signal canceller comprises: a first coupler for attenuating a part of the transmission/reception signal Tx+Rx which is input to the transmission signal canceller to branch the same and simultaneously performing a 90xc2x0 phase delay; a first variable band rejection filter for canceling the reception signal Rx and passing through only a transmission signal Tx with respect to a low power transmission/reception signal Tx+Rx which has been branched via the first coupler; a signal amplifier for amplifying the transmission signal Tx of the first variable band rejection filter into the same magnitude as that of the incoming transmission signal Tx; phase delay means for delaying a time so that the transmission/reception signal Tx+Rx unbranched in the first coupler is consistent with the inverted signal of the branched transmission signal Tx; and a second coupler for 90xc2x0 phase delaying the output signal of the signal amplifier additionally, and recombining the phase delayed result with the output signal Tx+Rx of the phase delay means, to thereby offset the unbranched transmission signal Tx with the phase inverted transmission signal xe2x88x92Tx and output only the reception signal Rx.
Also, the transmitter/receiver combination system further comprises at least one noise signal attenuation means for generating a signal together with the transmission signal from the transmitter disposed between the transmitter and the circulator and attenuating only a noise signal of a reception band input to the receiver.
According to another aspect of the present invention, a transmitter/receiver combination system comprises: at least one noise signal attenuation means connected to the output of a transmitter, for attenuating only a noise signal of a reception band generated together with a transmission signal from the transmitter; a circulator for receiving the transmission signal from the noise signal attenuation means, transmitting the received signal to an antenna without causing a signal loss, and transmitting the reception signal received from the antenna to other ends without causing a signal loss; and a first variable filter for canceling the transmission signal input in an attenuated form as much as a predetermined magnitude via the circulator together with the reception signal and transmitting only a reception signal to a receiver.
According to still another aspect of the present invention, a transmitter/receiver combination system for combining a transmitter and a receiver into a single antenna in a wireless communication system, the transmitter/receiver combination system comprising: a first circulator for receiving a transmission signal from the transmitter, transmitting the received transmission signal to a next stage without causing a signal loss; a second circulator for receiving the transmission signal from the first circulator, transmitting the received signal to an antenna without causing a signal loss, and transmitting the reception signal received from the antenna to other ends without causing a signal loss; a first pad and a second pad for receiving a first transmission signal input in an attenuated form as much as a predetermined magnitude via the other end of the first circulator and a second transmission signal input in an attenuated form as much as a predetermined magnitude via the other end of the second circulator, and for converting the first and second transmission signals into two transmission signals whose magnitudes are same and phases are inverted with each other, respectively; and signal combination means for combining the output signals of the first and second pads, canceling the first and second transmission signals and transmitting only a reception signal to the receiver.
In this case, at least one of the first and second pads comprises an attenuator for attenuating the magnitude of a transmission signal in the same magnitude as that of the other transmission signal; and phase delay means for delaying the phase of the signal in order to have a 180xc2x0 phase difference with respect to the other transmission signal.
According to a further aspect of the present invention, a transmission signal canceling method in a transmitter/receiver combination system for combining a transmitter and a receiver into a single antenna in a wireless communication system, the transmission signal canceling method comprising the steps of: (a) receiving a transmission signal from the transmitter, transmitting the received transmission signal to an antenna via a first path without causing a signal loss, and transmitting a reception signal received from the antenna via a second path; (b) 90xc2x0 phase delaying for delaying part of the transmission signal the reception signal input to the receiver in an attenuated form as much as a predetermined magnitude via the second path and branching the phase delayed result into a third path; (c) canceling the reception signal among the transmission signal and the reception signal which branched via the third path, and amplifying the transmission signal in the same magnitude as that of the second path; (d) delaying the transmission signal and the reception signal of the unbranched second path to have a phase difference of 180xc2x0 from the transmission signal of the branched third path; and (e) combining the phase inverted transmission signal of the third path with the phase delayed transmission signal and reception signal of the second path, canceling the transmission signal Tx and transmitting only a reception signal to the receiver.
According to still a further aspect of the present invention, a transmission signal canceling method comprising the steps of: (a) transmitting a transmission signal received from the transmitter, via a first path without causing a signal loss and generating a first transmission signal which has been attenuated as much as a predetermined magnitude via a second path; (b) transmitting the received transmission signal to an antenna without causing a signal loss, and transmitting the reception signal received from the antenna to a third path without causing a signal loss; (c) receiving the first transmission signal via the second path, and a second transmission signal input in an attenuated form as much as a predetermined magnitude via the third path by the transmission signal together with the reception signal, and converting the first and second transmission signals into two transmission signals whose magnitudes are same and phases are inverted with each other; and (d) combining the outputs of the second and third paths so that the first and second transmission signals are cancelled.
As described above, the present invention offsets a transmission signal incoming to a receiver together with a reception signal is cancelled by generating a 180xc2x0 phase inverted transmission signal with the same magnitude and delay time as those of the incoming transmission signal, to thereby improve a frequency separation degree of the transmitter and the receiver, reduce a coupling loss and simultaneously to reduce volume and cost thereof.
In the present invention, the transmission/reception frequency of the transmission/reception signal and the pass bands of the first through third variable filters are varied, or the transmission/reception band frequency is used in a frequency variable communication system or a secret conversation communication system, which is inverted with each other. Further, the present invention can secure a sufficient separation degree of the transmitter/receiver portion, with a result that a low power variable filter can be used.